I believe setting --backup-test-samples=0 will cause NO post backup verification to happen.
As you suggest, running a manual verification is a good idea if the automated one is disabled. The topic below should help you get that going. Note that Duplicati automatically tests random parts chosen from the set of parts LEAST recently tested. So if you have 100 parts and run the “test 1 part please” process 100 times, Duplicati will make sure it tests each part once rather than potentially testing some parts no times and others more than once.